This invention relates to rotating disk files of the type in which the read/write transducer is in contact with the disk surface when the disk is at rest and "flies" above the disk surface when the disk is rotating at its operating speed, and in particular to an apparatus and method for starting the rotation of the disk to prevent damage to the disk and/or transducer caused by the transducer sticking to the disk surface.
In many types of rotating disk files, the read/write transducers or heads are supported on a slider which rides on a cushion or bearing of air above the disk surface when the disk is rotating at its operating speed. The slider is connected to a linear or rotary voice coil actuator by means of a relatively fragile suspension. In large capacity magnetic recording disk files there is generally a stack of rigid disks and a number of actuators with each actuator supporting a number of sliders. The actuators move the sliders radially between the disks so that each head may access the recording area of a respective disk.
In these conventional disk files the slider is biased against the disk surface by a small force from the suspension when the disk is not rotating. The slider is thus in contact with the disk surface from the time the disk file is turned on until the disk reaches a speed sufficient to cause the slider to ride on the air bearing. The slider is again in contact with the disk surface when the disk file is turned off and the rotational speed of the disk falls below that necessary to create the air bearing. In such disk files a lubricant is often maintained on the disk surface to prevent damage to the head and the disk during starting and stopping of the disk. A serious problem with such disk files is that after the slider has been in stationary contact with the disk surface for just a short period of time, the slider tends to resist translational movement or "stick" to the disk surface. This "stiction" is caused by a variety of factors, including static friction and viscous shear forces and surface tension created by the lubricant between the disk and the slider. Even in those disk files which have disks with extremely smooth unlubricated disk surfaces, stiction may occur because of the strong intermolecular attraction at the interface between the smooth disk and slider surfaces. This stiction can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension.
In one known technique to overcome the stiction problem, disk rotation is started very slowly so that the slider breaks free from the disk surface gradually. This approach has the disadvantages that it requires a relatively long period of time to bring the disk file up to operating speed and that it imparts tangential forces to the suspensions, which is the direction where they are structurally weakest.